The present invention relates to an improved valve pilot-control unit for a brake-pressure modulator.
DE 100 09 116 A1 (hereinafter, “D1”) describes a known valve device for the pilot-control unit of a brake-pressure modulator for an electronic air-brake system (EBS). As shown in FIG. 2 of D1, the pneumatic circuit for the pilot-control unit of a brake-regulating loop of the brake-pressure modulator comprises a 3/2 solenoid valve (21) as a redundancy valve, a normally open 2/2 solenoid valve (22) as an air-admission valve and a normally open 2/2 solenoid valve (23) as a vent valve. As described in DE 42 27 084 A1 (see FIG. 2 therein), the redundancy valve in such circuit can also be used commonly for a second brake-regulating loop. According to this circuit layout, therefore, the pilot-control unit for two brake-regulating loops comprises one 3/2 redundancy valve for both loops and separate 2/2 vent valves and 2/2 air-admission valves for each individual loop. A total of 5 solenoids is provided for actuating the respective armatures of these 5 solenoid valves.
FIG. 4 of D1 shows that the solenoid valves according to FIG. 2 can be constructed with only one sealing seat forming a hermetic seal, at which, while the solenoid is deenergized, an elastomeric insert (41) provided in the corresponding armature (39) is urged by the action of the solenoid restoring spring (40) against a first stroke limiter having a valve-sealing seat (31) (47 for valve 21 of 3/2 type, 43 for valve 23 of 2/2 type, no sealing seat corresponding to 45 for valve 22 of 2/2 type). Besides this sealing seat, the solenoid valves have a second position in which the corresponding armature (39) is urged by the action of the magnetic force against a second stroke limiter (34) at which there is formed a detail metal valve seat (48 for valve 21 of 3/2 type, 46 for valve 22 of 2/2 type, no sealing seat corresponding to 44 for valve 23 of 2/2 type), which does not seal the unavoidable leaks hermetically but, because of the selected switching system, has no significance for the operation of the brake-pressure modulator.
DE-OS 24 03 770 discloses, for a hydraulic ABS solenoid valve, measures for influencing the magnetic forces, in order to obtain three stable and reproducible armature positions as a function of the magnet current, namely, positions for the deenergized condition, the condition for an “exciter stage 1” and the condition for a “full exciter stage”. In the deenergized starting position of the solenoid valve, outlet valve (12/27) is closed and inlet valve (11/28) is open; as a result, pressure source (3) is in communication with brake cylinder (2) and pressurization takes place in the brake cylinder. During energization corresponding to exciter stage 1, armature (13) travels a short distance and closes inlet valve (11/28), thus holding the pressure in brake cylinder (2). During energization corresponding to the full exciter stage, armature (13) is pushed up to spacer ring (16), outlet valve (12/27) opens and brake cylinder (2) is depressurized.
WO 03/053758 (hereinafter, “D2”) describes a brake-pressure modulator for a trailer vehicle, wherein a pilot-control unit containing four valves in the form of one 3/2 “reservoir/venting” selection valve (110), one 3/2 redundancy valve (109) and two 2/2 modulator valves (106/107) is used for two different brake-regulating loops. Therefore, the number of valves, and thus also the number of valve magnets, for two brake-regulating loops is reduced to four. However, the pilot-control circuit according to D2 suffers from the disadvantage that it is not possible at any given instant to admit air via one of the two ducts while venting via the other. Instead, at all times, it is only possible to admit air or vent via both ducts simultaneously. Consequently, it is not possible to raise the pressure in one duct and simultaneously lower the pressure in the other duct, as would be highly advantageous for a flexible regulation strategy. A further disadvantage of this solution lies in the series connection of the valves, meaning that the achievable air flow is diminished and the effective nominal width of the pilot-control unit is reduced.
DE 35 01 708 A1 describes an electromagnetically actuatable multi-way valve in which two different valves, one of which is an inlet valve (9, 10) that can be actuated via a first armature (5) and the other of which is an outlet valve (23, 25) that can be actuated via a second armature (21), can be loaded by only one common coil (2). Armatures (5) and (21) are biased with restoring springs of different dimensions, one a weakly dimensioned restoring spring (13) for armature (5) and the other a strongly dimensioned restoring spring (17) for armature (21), so that they can be actuated independently of one another by controlling the current in coil (2). This valve can therefore also be used as a combined air-admission/vent valve in a brake-pressure modulator. As explained below, however, the principle of different design of the restoring springs (13, 17) that underlies this valve for independent actuation leads to difficulties in valve design. The “weak” restoring spring must be able to overcome the gas force acting at inlet (9, 10) and it must therefore be strong enough that the restoring function for inlet valve (9, 10) is assured if the current fails. “Strong” restoring spring (17) must be strong enough that outlet valve (23, 25) is activated only at much higher magnet current than is the case for inlet valve (9, 10). The strong design of restoring spring (17) is therefore also limited by the force that the magnet can actually provide. To implement this principle, therefore, it is also necessary to provide a relatively large magnet with the necessary magnetic force. Besides causing higher manufacturing costs, such a magnet must be supplied with greater electrical power, which nevertheless does not lead to a satisfactorily short valve switching time, because of the increase of inertia related to structural size. In addition the choice of larger structural units works against the goal of producing compact devices.